1. Field of the Invention
The present invention relates to a separator for an electric double-layer capacitor, the electric double-layer capacitor, and a manufacturing method of the separator for the electric double-layer capacitor.
2. Description of the Related Art
An electric double-layer capacitor is also called an electric double-layer condenser, has a large capacity of a farad level, is superior in a cyclic property of a charging/discharging, and can be rapidly charged, so it is used for usages such as a backup power source of electronic appliances and a vehicle mount battery (energy buffer).
An outline of the electric double-layer capacitor will be described, referring to FIG. 5, which is a section view showing a basic configuration of the electric double-layer capacitor.
An electric double-layer capacitor 101 has, as shown in FIG. 5, a configuration where a container 102, a pair of polarizable electrodes 104 disposed with opposing separators 103 for the electric double-layer capacitor within the container 102 (hereinafter abbreviated to the ‘separator’ as needed), and a pair of current collectors 105 are housed. And within the container 102 an ion conductive electrolytic solution is injected. The electric double-layer capacitor 101 is a so-called secondary battery that repeats the charging/discharging with making charges (shown in symbols of + and − in FIG. 5), which are generated at an interface between the polarizable electrodes 104 and the electrolytic solution, a dielectric by an absorption/desorption of electrolytic solution ions to the polarizable electrodes 104 that are solid.
And for the separators 103 are necessary such an insulation property so as not to generate an electric leak between the polarizable electrodes 104 disposed at both sides of the separators 103, a high wetability for the electrolytic solution so that ions injected in the electrolytic solution can freely move, and thinness so as to be able to be housed more, for example, in a winding electric double-layer capacitor and the like.
Conventionally, as the separator for the electric double-layer capacitor are used mixed paper obtained by mixing the fibers such as olefin resins (for example, polyethylene, polypropylene, and the like), a cellulose, a polyester, and an aramid, and making paper from them (for example, see pages 3 to 5 in Japanese Patent Laid-Open Publication Hei 9-31883, pages 4 and 5 in Japanese Patent Laid-Open Publication 2001-244150, and pages 3 to 5 in Japanese Patent Laid-Open Publication 2001-185455).
Furthermore, these years an organic solvent such as propylene carbonate, which is high in withstand voltage, is used as a solvent of an electrolyte in order to make the electric double-layer capacitor a large capacity. With respect to such a manufacturing process of the electric double-layer capacitor, in order to further heighten the withstand voltage and an energy density, the electrolytic solution is injected after moisture, which is low in withstand voltage and easy to be electrolyzed, is completely removed, and electrodes, separators, and the like are sufficiently dried.
Accordingly, the separator used for the electric double-layer capacitor is desirable to have a sufficient heat resistance for enduring a drying process, and generally, the separator formed of an aramid fiber and polyester fiber having the heat resistance is widely produced and used.
However, the aramid fiber, the polyester fiber (for example, polyethylene terephthalate), and the like is an aromatic synthetic fiber containing a benzene ring. Accordingly, there is a problem that due to an influence of hydrophoby which the aromatic synthetic fiber has, the separator becomes low in wetability for the electrolytic solution where such the propylene carbonate, which is strong in hydrophily, is made a solvent.
Consequently, are strongly requested a separator for an electric double-layer capacitor that is high in wetability for the electrolytic solution and has the heat resistance and flexibility, the electric double-layer capacitor comprising the separator, and furthermore, a manufacturing method of the separator for the electric double-layer capacitor that is good in workability and excellent in productivity.